The inventive subject matter disclosed herein relates to light sources for use in industrial processes, such as for causing material transformation. The following description relates to one representative use of a solid-state light source. In certain aspects, the inventive subject matter disclosed herein relates to systems and methods directed to techniques for providing a fluid flow in association with a work surface that is the subject of a reactive process in the presence of light energy. Other aspects of the inventive subject matter are disclosed in the attached Appendix.
Light can be used to initiate various chemical reactions. Such light-initiated processes are a critical part of a number of industrial processes. The applicability of light as part of a particular process depends on several key properties of the light source, including, as examples, total optical power emitted by the source, wavelength(s) emitted by the source, source coherence, radiance of the source (power/area×steradian), degree of collimation, and power stability.
A particular application of light that has significant economic implications in today's industrial application is the polymerization, curing or other reaction as to adhesives and other light sensitive materials. The application of light may contemplate that the materials be irradiated through low transmittance layers. The application of light may contemplate that one or more specific wavelengths be employed. The application of light may contemplate that the light catalyze the reaction. The application of light generally contemplates that the light be absorbed by one or more materials employed in the process (e.g., adhesive). The application of light tends to also contemplate that the light either not be absorbed by one or more materials employed in the processed and/or, if absorbed undesirably, that any thermal or other undesirable aspects of that absorption be addressed (e.g., mitigation of undesirable heating of a work object). In any case, the application of light in association with the material that is to be bonded, sealed, or chemically altered by a polymerization or other reaction (e.g., with or without catalysis) presents a significant hurdle, and opportunities for advancement, in a number of industrial applications today.
In some chemical reactions, the presence of oxygen is detrimental to the chemical reaction. The detrimental effect of oxygen is well known in the industry. For example, a paper entitled “Nitrogen Inerting Benefits Thin UV Coating Cure,” by Dr. L. Misev of Ciba Specialty Chemicals Inc., proposes that:
The presence of oxygen during the UV cure process can have a detrimental effect on the cure response of free radical systems. Oxygen reacts with the free radical and forms peroxy radicals by reaction with the photoinitiator, monomer or propagating chain radical. The reactivity of the peroxy radicals is insufficient to continue the free radical polymerization process, leading to chain termination and an under cured system.
Thin coatings, typically printing inks and overprint varnishes, are particularly affected because oxygen replenishment is most effective in the few micrometers below the film surface. This counteracts the increased photoinitiator radical formation resulting from highest UV light intensity at the film surface. Therefore, when UV curing takes place in air the degree of double bond conversion does not depend only on the light intensity distribution within a coating according to the Beer-Lambert law.
The degree of benefit from inerting, typically by nitrogen purging of the UV exposed ink or coating surface, depends on various factors and can be best determined under the specific processing conditions.
According to Dr. Misey, a technique for overcoming the problem of oxygen-inhibited cures is by removing the oxygen by smothering the coating surface with an oxygen-free gas, such as nitrogen.
Certain inerting techniques are proposed in other technical literature. For example, a paper entitled “Progress in Organic Coatings, Overcoming oxygen inhibition in UV-curing of acrylate coatings by carbon dioxide inerting: Part II,” by K. Studer et al proposes:
The most effective way to overcome oxygen inhibition is to work in an inert atmosphere, by flushing the UV oven with nitrogen [6,7] or carbon dioxide [8]. The latter gas being heavier than air, it can be easily maintained in a container. As described by K. Studer et al., then, a common technique for inerting is to flush a container, apparently to immerse a work object in an inert atmosphere of nitrogen or carbon dioxide.
References to other technical literature appears to indicate that certain nitrogen-inerting techniques are known. See, for example, “DYNAMIC MECHANICAL ANALYSIS OF UV-CURABLE COATINGS WHILE CURING,” by R. W. Johnson, DSM Desotech Inc., Elgin, Ill. 60120; R. Muller, in: Proceedings of the RadTech Europe Conference, 2001, p. 149 (referenced in Studer et al. as [6], as set forth above); and T. Henke, in: Proceedings of the RadTech Europe Conference, 2001, p. 145 (referenced in Studer et al. as [8], as set forth above.
In some circumstances, it is either unsafe or impractical to immerse a work object in an oxygen-depleted, inert atmosphere. For example, when the work object is in an environment that must be shared with people, such inerting would be unsafe to those people. In other situations, immersion inerting might be impractical, for example, when the work object is part of, or moved by, a fast-moving mechanical assembly. In these other situations, the moving machinery will tend to undesirably mix, distribute, or disperse the inerting atmosphere (e.g., mixing the inert atmosphere with oxygen, tending to be work at odds with the depletion function), and/or may require adaptable gaskets and seals for effective isolation (i.e., with attendant-ramifications, e.g., expenses, maintenance, etc.).
Such a situation is encountered when curing adhesives used for bonding materials together to form optical storage media. Representative of such media are a compact disk (CD) or digital versatile/video disk (DVD). A CD or a DVD (CD/DVD) is generally formed from two disc-shaped transparent pieces of material. The flat surface of one or both of the discs is typically coated with a reflective surface, which is typically formed from a metal. The coated, flat pieces are conventionally bonded together using a UV-curable adhesive resin.
FIGS. 2A-2C respectively depict cross-sectional views of three exemplary conventional DVDs 210, 220 and 230. Such conventional DVDs have a cross-section that is similar to a conventional CD. In particular, FIG. 2A depicts a cross-sectional view of a portion of a one-sided single-layer disc 210, which is commonly referred to as a DVD-5. A DVD-5 can contain up to 4.38 GBytes of data. As shown in FIG. 2A, DVD 210 includes two layers 211 and 212 of polycarbonate (PC) material that are each typically 600 microns thick. Sandwiched between polycarbonate layers 211 and 212 are a UV-curable resin layer 213 that is typically 20-50 microns thick and an aluminum layer 214 that is typically 45-60 nm thick. FIG. 2B depicts a cross-sectional view of a portion of a single-sided dual-layer disc 220, which is commonly referred to as a DVD-9. A DVD-9 can contain up to approximately 7.95 GBytes of data. Disc 220 includes two layers 221 and 222 of polycarbonate material that are each typically 600 microns thick. Sandwiched between polycarbonate layers 221 and 222 are an aluminum layer 223 that is typically 50-60 nm thick, a UV-curable resin layer 224 that is typically 40-70 microns thick, and a layer 225 formed from silicon, silver or gold that is typically 10-15 nm thick. FIG. 2C depicts a cross-sectional view of a portion of a dual-sided DVD disc 230, which is commonly referred to as a DVD-10. A DVD-10 can hold up to 8.75 GBytes of data with 4.38 GBytes on each side. Disc 230 includes two layers 231 and 232 of polycarbonate material that are each typically 600 microns thick. Sandwiched between polycarbonate layers 231 and 232 are a first aluminum layer 233 that is typically 50 nm thick, a UV-curable resin layer 234 that is typically 40-70 microns thick, and a second aluminum layer 235 that is typically 50 nm thick. These are representative optical storage discs and it is contemplated that these and other constructions vary depending on various factors (the factors including, e.g., the type and production facility). For example, in the constructions above, the reflective layer is sometimes chosen to be silicon.
A central aspect of the construction of optical storage media is that the components thereof are bonded together with adhesives. This aspect is understood to remain even though the materials or other nature of the components may change (e.g., as the industry moves to other standards like Blue Ray and HD-DVD (High Density Digital Versatile/Video Discs).
In a CD/DVD, the UV-curable adhesive resin directly between the two polycarbonate layers preferably is isolated from oxygen in the surrounding atmosphere and, therefore, the adverse effects caused by the presence oxygen may be eliminated. Even in that case, when the two polycarbonate layers are placed together with the UV-curable resin disposed in between, some of the resin may seep from, flow out of or otherwise be established outside the two polycarbonate layers and, therewith, form a bead on or along one or more circumferential edges of the polycarbonate layers (e.g., on or along the outside edge). The bead of resin on or along the edge may tend to be exposed to oxygen during the curing process. Depending on the particular resin used and the exposure to oxygen, incomplete curing may occur, producing an undesirable, “tacky” edge of the resulting CD/DVD.
The machinery used to manufacture CD/DVDs is complex and includes rapidly moving parts. Accordingly, this machinery is understood to be generally incompatible with immersion inerting, as proposed in the technical literature.
Another problem associated with CD/DVD manufacture is thermal loading of the polycarbonate layers when the adhesive resin layer between the polycarbonate layers is cured. Thermal loading of the polycarbonate layers may lead to deviations, or distortions, of the resulting CD/DVD (e.g., in the axial, lateral and thickness dimensions) that, in turn, generally leads to poor read/write characteristics of the resulting CD/DVD. Thermal loading may also result in undesirable chemical properties of the materials involved (e.g., modification of those properties). Additionally, as the CD/DVD industry migrates towards lower initiator concentrations and shorter wavelengths (higher energy radiation) for reading and writing information on CD/DVDs, two different power densities may be employed during adhesive curing operations: one power density for an aerobic environment (i.e., the oxygen-present environment at the edge of a CD/DVD) and another power density for an anaerobic environment (i.e., the oxygen-reduced or oxygen-lacking environment internal to the CD/DVD).
In other cases of curing, the desired results may be characterized and have parameters other than those desirable to manufacture of CD/DVD. As an example, in curing acrylate inks in digital graphics, the desired finish is to be dry and should have a high gloss. This can be achieved by dissipating a large amount of energy into the polymer ink formulations and/or by inerting methods. The print media tends to be composed of a variety of materials, and some can be addressed by a higher energy method, which methods generally are incompatible with other materials, e.g., plastics like polyvinylchloride, polyethylene, polypropylene, as well as various heat sensitive substrates.
The aforementioned challenges and problems in manufacturing optical storage media and digital graphics are representative of problems and challenges in industrial processing, particularly processing in the presence of light. Accordingly, there is a need for methods and systems that provide improved environmental conditions so as to foster such processing. Without limiting the more general need set forth above, as illustrated via the representative problems identified above, there is a need for inerting selected portions of a work piece or substrate. As an example, such inerting may be at a surface or edge of a work piece or substrate (e.g., a rapidly moving work piece or substrate) having associated therewith, or comprising, light curable materials, which materials may include UV-curable materials, such as inks, coatings, or adhesives, such that, a reaction is properly effected (e.g., the reaction initiates, proceeds and/or is completed without or substantially without detrimental effects, such as those caused by the presence of oxygen or other inhibitor, or other impurity, contaminant or material, if present or present at or above a particular metrics, will be at odds with the reaction).
Additionally, a technique is needed for providing light in the context of the above inerting. Additionally, a technique is needed for providing variable light attributes during a photoreaction for a substrate or work piece that has different, environmental, physical or chemical properties, for example, a work piece or substrate having an aerobic environment and an anaerobic environment.
What is needed is a technique for enabling a reaction at or below a surface of a work piece, in which a fluid flow is provided in association with such surface of the work piece and, in the context of the work piece being exposed to a light, the reaction is fostered at or below the surface of the work piece. In additional, what is needed is a technique for enabling a reaction, as stated above, wherein the reaction is a photoreaction relating to the light exposure.